Various types of containers are employed to store chemicals. The composition of such containers is typically a function of the type of chemical stored and the anticipated use for the chemical.
Various mixtures and compounds are employed in chemical processes. Some are very stable and non-toxic. Others are quite volatile and unstable. Some present little, if any, risk to humans. Others are quite dangerous. Unstable compounds and mixtures can produce by-products, some of which are safe and others are dangerous.
By way of example, hydrogen peroxide is a chemical compound that is highly soluble in water. Various hydrogen peroxide mixtures (i.e., solutions) are employed as a bleach, deodorizing agent, antiseptic, disinfectant, or other purposes. Pure hydrogen peroxide solutions, completely free from contamination, are highly stable. However, trace impurities such as copper, iron, other transition metals and other materials can have a catalytic effect causing the hydrogen peroxide to decompose into water and oxygen.
Oxygen is less soluble in water than hydrogen peroxide. Thus, aqueous solutions of hydrogen peroxide tend to outgas oxygen as the hydrogen peroxide decomposes.
Despite its stability, hydrogen peroxide presents specific hazards. Hydrogen peroxide in high concentrations is a strong oxidizing agent that will react vigorously at ambient temperatures when stored in contact with cellulosic and other organic compounds. It is, therefore, generally recommended that hydrogen peroxide be stored in well ventilated, cool areas. Yet this is not always practical. Concentrated hydrogen peroxide solutions and hydrogen peroxide vapor are corrosive and strongly irritating to humans.
All of these characteristics of hydrogen peroxide must be considered when designing a suitable package for containing this compound. Likewise, the package must be designed to permit the hydrogen peroxide mixture to be extracted safely from the package for use.
In the past, hydrogen peroxide has also been used as a sterilant. Various packages have been employed in the prior art for storing the hydrogen peroxide, shipping the hydrogen peroxide and dispensing the hydrogen peroxide sterilant into a sterilization chamber. Examples of such prior art packages are shown in U.S. Pat. No. 4,817,800 granted Apr. 4, 1989 to Williams et al; U.S. Pat. No. 5,882,611 granted Mar. 16, 1999 to Williams et al; U.S. Patent Application Publication No. 2005/0263422 dated Dec. 1, 2005 and U.S. Pat. No. 7,101,52 granted Sep. 5, 2006 to Hahs et al. Each of these packages comprises a flat, rectangular cassette made of plastic or other suitable material. The cassette includes walls forming a plurality of compartments. Positioned in each compartment is a cell. The cells are formed using two sheets of plastic having mating recesses therein. The peripheries of the recesses are bonded together to form a series of cells held together as a single cell pack in a fashion similar to bubble wrap packaging. The cell pack is then captured between mating portions of the cassette so that each cell is securely gripped in an individual compartment and each compartment is separated from the others. A small, predetermined quantity of the liquid sterilant is contained in each cell. Each compartment has a pair of holes through the plastic walls of the compartment. To extract the sterilant from a cell, a needle is inserted through a lower hole. This needle punctures the cell within the compartment. The sterilant is then extracted through the lower hole in the compartment using pressure which is applied through an upper hole in the compartment to force the sterilant out the cell (and compartment) through the lower hole in the compartment.
Packages of the type described in the above-referenced patents have a number of disadvantages. First, the multi-cell package design contributes to the complexity and expense of the unit used to extract sterilant from the individual cells of the package. Either the needle or the package must be moved to precisely align a hole in a particular compartment with the needle of the extraction device. Only when such precise alignment is achieved can the needle be inserted into the hole, puncture the cell of the compartment and extract the contents. Such alignment is required for each of the compartments of the package. Similar issues arise when filling multiple cells with sterilant.
Second, when the package of the type shown in these prior art patents is employed, the extraction system must employ some logic and control scheme so the system knows which cells have been evacuated and which cells still contain sterilant. The filling system must employ similar logic and control.
Third, the design of the packages shown in the above-referenced patents makes the packages susceptible to improper placement in an extraction device. The outer walls of the container form a rectangle. Yet the structures contained within the rectangle dictate that the package have a top, a bottom, a front and a back. The package is, therefore, susceptible to being inserted in a filling station or an extraction station either upside down, backwards or both, unless special provisions are added to key the cartridge in the station.
Fourth, filling multiple smaller cells with a specific amount of liquid to achieve a total volume of liquid is less accurate than filling one larger cell.
Fifth, the prior art is overly complex requiring both pressure and vacuum sources to remove the contents of a cell.
The small size of the individual cells and compartments presents still other problems. The contents of a single cell are likely insufficient to complete a sterilization cycle. Use of the contents of multiple cells may add to the time required for sterilization. If the contents of all of the cells are not used during a sterilization cycle, the result may be undue waste of the sterilant or disposal problems. If one tries to deal with these problems by using the remaining sterilant in the next sterilization cycle, other problems can arise, particularly if the sterilant remaining in the package is insufficient to complete the next cycle.
Other problems can arise from the size and geometry of the cells of the packages in the prior art patents. The ratio between the volume of sterilant each individual cell contains and the surface area of the plastic forming the cell results in increased chemical and physical interaction between the sterilant and the plastic. When hydrogen peroxide is used as a sterilant, its strong oxidizing characteristics can lead to decomposition of the plastic. Likewise, the plastic can present impurities that catalyze the decomposition of hydrogen peroxide into water and oxygen. The prior art packages do not address the inevitable build-up of oxygen gas in the package. This can occur in different cells at different rates leading either to non-uniform cell failure or non-uniform decomposition of hydrogen peroxide to the point where it can no longer be effectively used as a sterilant.